The invention relates to knee joint prostheses and more particularly to knee joint prostheses and components thereof having improved fixation and stability of the tibial bearing insert to the tibial tray.
Joint replacement surgery is quite common and enables many individuals to function normally when otherwise it would not be possible to do so. Artificial joints are normally composed of metallic, ceramic and/or plastic components that are fixed to existing bone.
Knee arthroplasty is a well known surgical procedure by which a diseased and/or damaged natural knee joint is replaced with a prosthetic knee joint. Typical knee prostheses include a femoral component, a patella component, a tibial tray or plateau, and a tibial bearing insert. The femoral component generally includes a pair of laterally spaced apart condylar portions, the distal surfaces of which articulate with complementary condylar elements formed in a tibial bearing insert.
The tibial tray is mounted within the tibia of a patient. Typically, the tibial bearing insert, which is usually made of ultrahigh molecular weight polyethylene (UHMWPE), is mounted upon the superior surface of the tibial tray through mechanical interlocking. Load and stress is placed on the knee prosthesis, and particularly on the tibial bearing insert, during normal daily use and may lead to displacement or dislocation of the insert from the tibial tray. Tibial bearing inserts that are specifically designed for revision knee prostheses as well as those designed to compensate for colleratal ligament deficiency are particularly susceptible to loads and stresses that could cause dislocation or displacement of the tibial bearing insert. Such inserts usually have a protruding eminence on the superior surface of the insert, which is designed to limit varus and valgus movements of the knee joint. In deep flexion of the joint (e.g., 90.degree.-120.degree. ) the femoral component exerts a high anteriorly directed load component on a posterior facing wall of the eminence. As noted above, this force component can lead to dislocation or displacement of the tibial bearing insert.
Several techniques are known to reinforce or mate the tibial bearing insert to the tibial tray. For example, U.S. Pat. No. 4,822,366 affixes the tibial bearing insert to the tibial tray using a nut and a cooperating bolt. A similar design, which relies upon a threaded locking screw to reinforce the mating of the tibial bearing insert and the tibial tray, is disclosed in U.S. Pat. No. 4,936,853.
Other reinforcement designs rely upon threaded screws to help secure the tibial insert to the tibial tray. One disadvantage of such designs is the potential that the threading of the screw through the polymeric insert could increase the potential for developing wear debris within the joint. Wear debris results as minute particles of debris (e.g., metal or plastic from the prosthesis) become dislodged and migrate within the joint. The phenomenon of wear debris within artificial joints is a serious problem that can inhibit the proper mechanical functioning of the joint. Moreover, wear debris can lead to osteolysis and bone deterioration. When wear debris develops within an artificial joint, surgical removal of the debris or subsequent replacement of the artificial joint is often necessary.
There is thus a need to provide alternative mechanisms and devices for reinforcing the securement of a tibia/bearing insert to a tibial tray in a knee prosthesis.
Accordingly, it is an object of the present invention to provide knee prostheses in which securement of the tibial bearing insert to the tibial tray is reinforced. A further object is to provide an effective reinforcing pin that reduces the load exerted on the tibial bearing insert by the femoral component. It is also an object to provide a knee prosthesis in which some of the load directed to the tibial bearing insert can be transferred to the tibial tray. Another object is to provide a reinforcement pin for increasing the strength of attachment of the tibial bearing insert to the tibial tray. It is also an object to provide improved knee prostheses that are better able to withstand the forces associated with normal daily activities. These and other objects of the invention will be apparent to those having ordinary skill in the art upon reading the disclosure that follows.